The present invention relates to modems generally and to generally secure point-to-point modems in particular.
Personal computers are known in the art and have been widely available for some years. They are becoming more and more popular in the office and at home, especially for communication purposes, whether to send electronic mail, to xe2x80x9csurfxe2x80x9d the World Wide Web on the Internet or to talk via the Internet. Unfortunately, such actions leave the computer vulnerable to attack from the outside. There are several solutions to the problem, all of which operate at the higher layers of communication.
One solution is a xe2x80x9cfirewallxe2x80x9d which considers a selected connection and determines if such a selection is of the allowable type. If the desired connection is not allowed, the communication is closed. This solution operates at the application layer (layer 7).
Other solutions operate at the presentation, or sixth, layer. One involves data encryption in which all data is encrypted to ensure that, if an unauthorized user receives the data, he cannot understand it. The second solution at this layer utilizes a password. Communication between two modems is only allowed if the user requesting the communication has the correct password.
Callback modems operate at the fifth, or session, layer. These modems provide an initial session in which a requesting user provides his password. The session is then closed and the callback modem xe2x80x9ccalls backxe2x80x9d to the phone number associated with the requesting user whose password was received. If the requesting user is at the phone number, the two modems will communicate. Otherwise, no communication will occur.
All of the above described methods permit a connection to occur and there are still chances that an intruder can break into the system being protected, despite the protection methods.
It is therefore an object of the present invention to provide a modem which attempts to prevent a communication session from being established except between two authorized users.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a modem including a symbol converting unit and a processing unit. The symbol converting unit converts between binary data and symbol data in accordance with a first constellation which is a transformed version of a standard constellation. The processing unit processes the symbol data for transmission and produces symbol data from received signals.
Additionally, in accordance with a preferred embodiment of the present invention, the modem includes a unit for generating the first constellation by placing symbols generally midway between at least two neighboring symbols of the standard constellation.
Moreover, in accordance with a preferred embodiment of the present invention, the transformed constellations are one of the following: translations, rotations and redefinitions of the standard constellations. The transformation can be half the size of a trellis subset. The present invention can include a unit for generating the first constellation by translating the standard constellation by more than half a symbol and also comprising unit for folding the constellation.
Alternatively, in accordance with a preferred embodiment of the present invention, the symbol converting unit can convert between binary data and symbol data in accordance with at least two different constellations. In this embodiment, the symbol converting unit can include a constellation changing unit for determining which constellation, of the at least two constellations, to utilize at any given time.
Moreover, in accordance with a preferred embodiment of the present invention, the modem can include a unit for maintaining the quality of modulation substantially the same as for the original modulation technique.
Furthermore, there is also provided, in accordance with a preferred embodiment of the present invention, a communication system including a host modem and at least one remote modem. The host modem includes a host unit for communicating via a constellation and a host unit for selecting one transformed constellation among a plurality of transformed constellations for use by the host unit for communicating. Each remote modem includes a remote unit for communicating via a constellation and a remote unit for activating the one transformed constellation for use by the remote unit for communicating.
Additionally, in accordance with a preferred embodiment of the present invention, the host unit includes a unit for indicating the selected transformed constellation to the at least one remote modem.
Moreover, in accordance with a preferred embodiment of the present invention, the remote modem includes a unit for identifying the remote modem to the host.
Further, in accordance with a preferred embodiment of the present invention, the host unit for selecting includes a unit for changing the transformed constellation after a predetermined number of symbols have been communicated. The unit for changing typically includes a unit for determining the time to change which typically uses at least one of the following as input: user identification, session duration, time and date.
Finally, the present invention includes the methods performed by the various modems and system described hereinabove.